Add support for rt-thread

SConscript

@@ -0,0 +1,19 @@
+from building import *
+import rtconfig
+
+# get current directory
+cwd     = GetCurrentDir()
+# The set of source files associated with this SConscript file.
+src     = Glob('csrc/*.c')
+src    += Glob('sys/rt-thread/port/*.c')
+src    += Glob('sys/rt-thread/examples/*.c')
+
+path    = [cwd + '/']
+path   += [cwd + '/csrc']
+path   += [cwd + '/sys/rt-thread/port']
+
+LOCAL_CCFLAGS = ''
+
+group = DefineGroup('u8g2s', src, depend = [''], CPPPATH = path, LOCAL_CCFLAGS = LOCAL_CCFLAGS)
+
+Return('group')